KR19980087218A - Active Multimode Optical Signal Splitter - Google Patents

Abstract

The active optical signal splitter compensates for the optical signal splitting loss. An active optical signal splitter includes an active multimode waveguide providing segmentation and amplification of an input optical signal, and a plurality of integrated single mode waveguides. Single mode waveguides may be formed of active and passive waveguide regions. Pumping current can be applied to the active single mode waveguide region to provide individual amplitude control of the N output optical signals. By providing segmentation and optical amplification of the input optical signal in an active multimode waveguide, the losses arising from the optical losses due to signal segmentation can be compensated, thereby splitting one optical signal into N optical signals with virtually no loss. It is possible to.

Description

Active Multimode Optical Signal Splitter

FIELD OF THE INVENTION The present invention relates to an optical signal splitter, and more particularly to an optical multimode waveguide that allows signal splitting and current pumping to provide optical power amplification to minimize optical losses due to signal splitting. A waveguide portion comprising an active multimode optical signal splitter and a passive region for supplying current pumping to provide individual amplitude control of the N output signals, and may also comprise an active region.

Photonic devices are known for use in a variety of applications, including antenna systems, such as phased array antenna systems, to provide beam steering of radiation patterns. For example, as disclosed in US Pat. Nos. 5,162,803 and 5,579,016, which are incorporated herein by reference, the staged array antenna typically includes a number of antenna elements configured in the array. In such a system, the RF modulated optical signal is divided into a plurality of component optical signals that alternately feed individual antenna elements in the array. The element optical signal supplied to each of the antenna elements is delayed by a time delay or by a phase delay to cause beam steering of the radiation pattern emitted from the antenna element.

Lightweight, compact, and mechanical compliance of photonic elements, such as optical waveguides, provides relatively low transmission loss, wide bandwidth, and insignificant RF scattering. Recent technological advances have improved the RF performance of optical modulators and demodulators for use with the staged array antenna system for higher frequencies and wider bandwidths.

For example, as disclosed in US Pat. No. 5,410,625, passive optical signal splitters are known for use in a variety of applications, including staged array antenna systems. Unfortunately, the passive optical signal splitter is generally not suitable for applications that are sensitive to signal-to-noise ratio degradation due to the relatively large RF signal attenuation that usually involves optical signal splitting. More specifically, in the system, the optical carrier is modulated by the RF voltage. If the optical carrier splits N times, the RF signal power is 1 / N²Decreases to The 1 / N coefficient is larger than the corresponding effect in a conventional RF distributed system. Despite the increased RF splitting loss in wide optical dispersion systems, a significant reduction in propagation loss in the optical waveguide for electrical microstrip waveguides results in a net reduction of losses in many systems, especially if high bandwidth and small size. And if light weight is desired, the optical system makes it more desirable.

Unfortunately, the losses associated with the optical signal splitters involve preamplification. However, the preamplification of the input signal is limited by the saturation power whose upper limit approaches the maximum optical power before the RF gain is reduced. To minimize the impact of signal shot noise, the signal is usually about 10 milliwatts or higher. If an optical preamplifier is used to compensate for splitting losses in a passive device, the output level is approximately 1 / N times saturation power by a 1 * N splitter to prevent the preamplifier from driving too strongly to saturation. It is known to be limited to the value of. However, this requires saturation power to be N * 10 milliwatts to maintain a 10 milliwatt signal output level.

It is an object of the present invention to solve various problems of the prior art.

It is another object of the present invention to provide an optical signal splitter which reduces the splitting loss.

Briefly, the present invention relates to an active multimode optical signal splitter that compensates for optical signal splitting losses. An active multimode optical signal splitter includes an optical multimode waveguide and a plurality of signal mode waveguides, which provide signal splitting and current pumping to provide optical power amplification to minimize optical losses due to signal splitting. Consider. Signal mode waveguides can be formed with active and passive waveguide regions.

Pumping current is applied to the active multimode waveguide to simultaneously provide optical amplification and splitting, and for an embodiment of the active region in the output waveguide, the pumping current is also used to provide individual amplification control of the N output signals. It can be applied to each active output waveguide. By providing optical amplification to the multimode optical waveguide, the benefit of optical preamplification is obtained without a penalty of the required increase in saturation power from about 10 Hz to N * 10 Hz. The loss due to the division can be compensated, so that it is possible to divide one optical signal into N optical signals with virtually no loss.

These and other objects of the present invention will be readily understood with reference to the following detailed description and the accompanying drawings.

1 is a schematic diagram showing an active multimode optical signal splitter according to the present invention as an example of 1 * N.

2A and 2B are cross-sectional views illustrating an active multimode optical signal splitter in accordance with the present invention showing different stages of the manufacturing process.

3 is a perspective view illustrating a known passive multimode splitter;

Explanation of symbols for the main parts of the drawings

20 optical signal splitter 24 input single mode waveguide

26: output single mode waveguide 28; Multimode waveguide

29: electrical contact stub 48,52: passive area

50: active area

The present invention relates to an active multimode optical signal splitter based on symmetric mode self-imaging effects. Light splitting into 1 to N output signals is achieved in multimode waveguides of length equal to 1 / N (Λ), where Λ is described by JM Heatan, RM Jenkins, DR Wright, JT Parker, JCH Birbeck, and KP Hilton. A New Form of Integrated 1-N Light Beam Splitter Using Symmetric Mode Mixing in GaAs / AlGaAs Multimode Waveguides by Appl. Phys. Lett., Vol. 61, No. 15, pp. 1754-1756, 1992). As described, the symmetric mode magnetic field distance. The output of the multimode waveguide is suitable for monolithic connection to N single mode waveguides, for example, spread into a space of 50 micrometers on a semiconductor chip. An important feature of the present invention is that signal splitting provides upfront optical amplification to provide optical power gain, as generally described in US Pat. Nos. 5,539,571 and 5,414,554, which are incorporated herein by reference. And an active multimode waveguide that also considers current pumping. Active multimode optical signal splitters also include single mode waveguides, which may be formed as passive waveguides or as active and passive regions. The active region of the single mode waveguide may include electrical contacts to provide individual amplification control of the output signal from the multimode waveguide. As described above, the active multimode optical signal splitter is suitable for dividing one optical signal into N optical signals with virtually no loss due to signal division.

An example embodiment of an optical signal splitter according to the present invention, generally identified by reference numeral 20, is shown in FIG. 1. Although optical signal splitter 20 is shown as a 1 * 8 optical signal splitter, it should be understood by those skilled in the art that the principles of the present invention may be applied to various types of signal splitters other than those shown and described. In addition, the size of the optical signal splitter 20 shown and described is an example for operation at an optical wavelength of 1.3 microns (μ) in InP / InGaAsP semiconductor materials.

Referring to FIG. 1, as described in more detail below, the optical signal splitter 20 is suitable for being monolithically fabricated on a semiconductor substrate such as InP. The optical signal splitter includes a multimode waveguide 28 that provides 1-N division of the input optical signal. Passive multimode waveguides as shown in FIG. 3 are generally known in the art and are incorporated herein by reference (GaMs by JM Heatan, RM Jenkins, DR Wright, JT Parker, JCH Birbeck, and KP Hilton). A New Form of Integrated 1-N Light Beam Splitter Using Symmetrical Mode Mixing in AlGaAs Multimode Waveguides: Appl. Phys. Lett., Vol. 61, No. 15, pp. 1754-1756, 1992 and RM Jenkins, RWJ A waveguide beam splitter and recombiner based on multiple propagation phenomena by Debereax, and JM Heatan: Optics Lett., Vol. 17, No. 14, pp. 991-993, 1992).

An important feature of the present invention is that the multimode waveguide according to the present invention is formed as an active device that provides optical gain as well as optical signal division. As shown in FIG. 1,

Optical signal splitter 20 includes an input single mode waveguide 24; A multimode waveguide gain cavity 28 of length Λ / N, where Λ is the symmetric mode magnetic field distance and N is the number of signal outputs; It also includes a plurality of output single mode waveguides 26. Electrical contacts (shown diagonally in FIG. 1) are formed on the multimode gain cavity 28 which considers current pumping to reduce signal noise and provide a prior gain that improves the saturation performance of the device. Optionally, electrical contact stub 29 may be connected to an electrical contact formed on multimode gain cavity 28 to facilitate external connection to the device in some applications. The optical signal splitter 20 may be formed from an input single mode waveguide 24 having a width of 3 microns and a length of 0.1 mm and has a length of about 1.26 mm for operation at an optical wavelength of 1.3 μm in InP / InGaAsP semiconductor material. Λ) and a plurality of output waveguides 26, which may be connected to an active multimode waveguide gain cavity 28, which may be formed to a width W of about 62 microns, and to which the output of the active multimode waveguide splitter is connected. Can be connected.

The output of the multimode waveguide 28 is monolithically connected to a plurality of single mode waveguides 32, 34, 36, 38, 40, 42, 44 and 46. The single mode waveguide of the device may be divided into three regions: first passive waveguide region 48, active waveguide region 50, and second passive waveguide region 52. For example, the first passive waveguide region 48 is 2.75 mm long while the active waveguide region 50 is 0.5 mm long and the second passive waveguide region 52 is 3.39 mm long.

Multiple electrical contacts 54, 56, 58, 60, 62, 64, 66, and 68 are connected to single mode waveguides 32, 34, 36, 38, 40, 42, 44, and 46 in the active waveguide region 50. Can be aligned and connected. Contacts 54, 56, 58, 60, 62, 64, 66 and 68 are single-mode waveguides 32, 34, 36, 38, 40 and 42 for individually providing on individual amplification control of the N output signals. Consider the current pumping of 44, 46.

An important feature of the present invention relates to an active multimode waveguide 28 that is used to compensate for optical signal loss due to splitting as well as providing improved saturation performance. More specifically, for example, as shown in Figure 3, conventional splitters, such as multimode splitters, are passive devices and require input signal preamplification. Unfortunately, the input signal preamplification is limited by the saturation power whose upper limit approaches the maximum optical power before the RF gain decreases. To minimize the impact of signal shot noise, the signal is usually about 10 milliwatts or higher. If an optical preamplifier is used to compensate for splitting losses in a passive device, the output level is approximately 1 / N times saturation power by a 1 * N splitter to prevent the preamplifier from driving too strongly to saturation. Often limited to the value of. However, this requires saturation power to be N * 10 milliwatts to maintain a 10 milliwatt signal output level. An important feature of the present invention is that the gain is supplied to the active waveguide 28 so that the luminous intensity never significantly exceeds the saturation intensity. Thus, the output signal level can approach saturation power, which requires only about 10 milliwatts to maintain a 10 milliwatt signal output. With this geometry, the benefit of optical preamplification prior to dividing into N outputs produces an optical amplifier with a saturation power N times higher than the desired output signal level, which requires more than 10 millimeters to minimize shot noise. Is achieved without this.

An important consideration is that the pumping current should be kept at the minimum level. More specifically, as is known in the art, semiconductors with optical gains exhibit spatial holes burning as optical power approaches saturation intensity. Multimode imaging can be influenced by the vigorously moving gain holes depending on the magnitude of the linewidth enhancement coefficient a and the optical power of the amplifier. Typically, the α value ranges from 2 to 4 for most semiconductor gain media. In order for the device to function properly, the optical gain will never exceed the saturation intensity required for good RF performance, and the effects of the vigorously moving gain holes in multimode imaging will not degrade the device's performance so much. It must be kept at the minimum level.

2A and 2B show a process for manufacturing the optical signal splitter 20 according to the present invention. Fabrication of optical signal splitter 20 may include a regrowth process that is typically required to integrate short active regions of semiconductor waveguides, such as passive waveguides, as shown in FIGS. 2A and 2B. Other manufacturing methods are also suitable for such things as selective local epitaxy. In particular, referring first to FIG. 2A, an optical signal splitter 20 according to the present invention may be formed on an n-doped substrate 70, such as an InP substrate. A n-doped waveguide layer 72, such as, for example, InGaAsP, is deposited on the substrate 70 by, for example, metal organic chemical vapor deposition (MOCVD) to be epitaxially grown to a thickness of 0.3 microns. Can be. An active layer 74 is then deposited, grown on top of the waveguide layer 72, and also to remove the large absorption loss associated with the unpumped active layer in the passive region 48, 52. This passive region (i.e., regions 48 and 52) can be removed by etching. The etching process also generally forms active regions 28 and 50 as shown in FIG. 2A. Various layers forming the active layer 74 may be deposited, for example, by MOCVD.

Since the passive regions 48 and 52 are formed by etching the active layer 74 and then regrowing, the active layer 74 is undoped, i.e., doped with a thickness of 0.025 microns deposited by MOCVD, for example. Not formed of InP. The active regions 28 and 50 of the waveguide are formed of quantum wells including a quantum well layer 82 sandwiched between two barrier layers 84 and 86. Quantum wells are deposited on top of the corrosion stop layer 80. Barrier layers 84 and 86 as well as quantum well layer 82 may be formed from each InGaAsP having a thickness of about 0.01 micron. Another waveguide layer 88 is formed on top of the upper barrier layer 86, for example formed from 0.045 microns of the SCH to optimize the transverse light mode. As is known in the art, in order to further provide optical gain, the quantum well layer 82 may be composed of a plurality of quantum well structures. The plurality of quantum well structures consist of two to twelve or more quantum well layers alternating with barrier layers.

Active layer 74 is etched by conventional techniques to make passive regions 48 and 52. The upper limiting layer 90 can then be deposited by MOCVD or other techniques, such as regrown on top of the etched structure. Constraint layer 90 may be a p doped layer formed from In having a thickness of 1.0 micron. Top layer 92 is formed from InGaAs doped with p +. The electrical contacts can then be formed to align with the active regions to provide current injection and light gain in these cross sections. Metal contacts 29, 54, 56, 58, 60, 62, 64, 66, and 68 can be formed by conventional photo plate techniques.

Clearly, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

Claims (17)

An active multimode optical signal splitter for compensating optical losses due to signal division, comprising: an active multimode waveguide optical signal splitter for dividing and amplifying one input optical signal into N output optical signals; An active multimode optical signal splitter comprising N single mode optical waveguides optically coupled to the mode waveguide. 2. The N single mode optical waveguide of claim 1, wherein the N single mode optical waveguides comprise at least one passive region and one active region, the active region receiving a pumping current allowing individual amplitude mode control of the N output signals. And an electrical contact connected to each of the N single mode waveguides for the active multimode optical signal splitter. The active signal splitter according to claim 1, wherein the optical signal splitter is a multimode waveguide having a length equal to Λ / N, wherein Λ is a symmetric mode self-imaging distance and N is the number of output signals. Multimode Optical Signal Splitter. 3. The active multimode optical signal splitter of claim 2, wherein the N single mode waveguides are configured such that a first passive region is optically coupled to the splitter. 5. The active multimode optical signal splitter of claim 4, wherein the active regions of the N single mode waveguides are optically coupled to the first passive region. 6. The active multimode optical signal splitter of claim 5, wherein a second passive region is optically coupled to the active region. 2. The active multimode optical signal splitter of claim 1, wherein the active multimode optical signal splitter is monolithically formed on a single substrate. An active multimode optical signal splitter for compensating optical loss due to signal division, comprising: an active multimode waveguide for optically dividing and amplifying one input optical signal into N output signals, and optically for the optical signal splitter An active multimode optical signal splitter comprising a plurality of optical signal mode waveguides connected to each other. 9. The method of claim 8, wherein the single mode waveguide is formed of one integrated active region and one or more passive regions, wherein the active region is formed of electrical contacts in contact with the plurality of waveguides, the active and passive regions of the An active multimode optical signal splitter characterized in that it is monolithically integrated in a multimode splitter. A process for manufacturing an active multimode optical signal splitter, (a) epitaxially growing a substrate layer, a waveguide layer and an active layer, (b) etching the active layer to form one or more active and passive regions defined by an etched structure; (c) forming a limiting layer on the etched structure, and also (d) forming an electrical contact in alignment with said at least one active region. 11. The process of claim 10 wherein InP is anywhere in the substrate layer. 11. The process of claim 10 wherein InGaAsP is anywhere in the waveguide layer. 11. The process of claim 10, wherein the active layer comprises a quantum well sandwiched between a pair of barrier layers. 11. The process of claim 10 wherein the active layer comprises a plurality of quantum well structures sandwiched between a pair of barrier layers. 11. The process of claim 10, wherein said limiting layer is formed by regrowth. 11. The process of claim 10, wherein the confinement layer is formed by selective epitaxy. 11. The process of claim 10, wherein the electrical contact is formed by photolithography.